Chromous acid

Fig. 9.3 Potential forms for the H-bond in so-called chromous acid, CrO(OH), left and deuterated, right. Reproduced from [7] with permission of Taylor Francis Ltd.

A description of the double well O-H-O bond in so-called chromous acid (in reality a Cr(III) compound, CrO(OH)) has been derived in agreement with some early INS work [7], see Fig 9.3. In symmetric H-bonds the vibrations are best described as, the symmetric stretch, VsCO-H-0), and the antisymmetric stretch, VasCO-H-O) wherev (O-H-O)... 

Chromous acid (chromium(III) oxide hydroxide) CrOOH FDS 55... 

J. Tomkinson, A.D. Taylor, J. Howard, J. Eckert J.A. Goldstone (1985). J. Chem. Phys., 82, 1112-1114. The inelastic neutron scattering spectrum of chromous acid at high energy transfers. 

The points lying farthest from the straight line are from 0—H.. 0 systems where a low potential barrier between the minima is expected. Those on the left side (0—H distance too small) correspond to oxalic acid dihydrate and potassium hydrogen oxalate with a symmetric double minimum (15,48), those on the right side (O—H distance too large to chromous acid with a symmetric double minimum (4,86). In all cases a delocalisation of the proton is likely (see the end of Section III). 

Isophorone usually contains 2—5% of the isomer P-isophorone [471-01-2] (3,5,5-trimethyl-3-cyclohexen-l-one). The term a-isophorone is sometimes used ia referring to the a,P-unsaturated ketone, whereas P-isophorone connotes the unconjugated derivative. P-lsophorone (bp 186°C) is lower boiling than isophorone and can be converted to isophorone by distilling at reduced pressure ia the presence of -toluenesulfonic acid (188). Isophorone can be converted to P-isophorone by treatment with adipic acid (189) or H on(Ill) acetylacetoate (190). P-lsophorone can also be prepared from 4-bromoisophorone by reduction with chromous acetate (191). P-lsophorone can be used as an iatermediate ia the synthesis of carotenoids (192). 

Ghromium(II) Compounds. The Cr(II) salts of nonoxidizing mineral acids are prepared by the dissolution of pure electrolytic chromium metal ia a deoxygenated solution of the acid. It is also possible to prepare the simple hydrated salts by reduction of oxygen-free, aqueous Cr(III) solutions using Zn or Zn amalgam, or electrolyticaHy (2,7,12). These methods yield a solution of the blue Cr(H2 0)g cation. The isolated salts are hydrates that are isomorphous with and compounds. Examples are chromous sulfate heptahydrate [7789-05-17, CrSO 7H20, chromous chloride hexahydrate... 

In 1979, a viable theory to explain the mechanism of chromium electroplating from chromic acid baths was developed (176). An initial layer of polychromates, mainly HCr3 0 Q, is formed contiguous to the outer boundary of the cathode s Helmholtz double layer. Electrons move across the Helmholtz layer by quantum mechanical tunneling to the end groups of the polychromate oriented in the direction of the double layer. Cr(VI) is reduced to Cr(III) in one-electron steps and a colloidal film of chromic dichromate is produced. Chromous dichromate is formed in the film by the same tunneling mechanism, and the Cr(II) forms a complex with sulfate. Bright chromium deposits are obtained from this complex. 

Acetoxy-17a-hydroxy-5a-pregnane-3,l 1,20-trione (40) is brominated in acetic acid under equilibrating conditions to give a solution of the 2a,4a-di-bromo compound (41). This is reduced by chromous chloride without further treatment, to the 4a-bromo compound (42). The recrystallized bromo compound (42) is then dehydrobrominated via the semicarbazone (43) which is converted without isolation into cortisone acetate (44) by treatment with pyruvic acid ... 

The 10l -acetoxy group can be red actively removed with zinc and acetic acid or chromous chloride to give I9-norsteroids in high yield. Thermal elimination (boiling tetralin) of acetic acid from the crude 10)5-acetoxy-A -3-ketone or treatment with methanolic alkali leads to aromatization of ring A. Estrone alkyl ethers are formed from 10)5-acetoxy-19-nor-A -androstene-3,17-dione by treatment with alcohols and perchloric acid. Similar aromatizations are observed with 5,10-oxido, 5,10-dihydroxy, 5,10-halohydrins or 5,10-dihalo-3-ketones. ... 

The groups R2N and Cl can be added directly to alkenes, allenes, conjugated dienes, and alkynes, by treatment with dialkyl-V-chloroamines and acids. " These are free-radical additions, with initial attack by the R2NH- radical ion. " N-Halo amides (RCONHX) add RCONH and X to double bonds under the influence of UV light or chromous chloride. " Amines add to allenes in the presence of a palladium catalyst. ... 

Chloro 6-trichloromethyl pyridine (N-Serve ) Chromates, certain insoluble forms Chromic acid and chromates (as Cr) Chromium, soluble chromic and chromous salts (as Cr)... 

Robinson et al. [263] have studied both at the laboratory and semi-technical scale the electrochemical generation of chromous ion (Cr(II)) for the reduction of sodium hydroxymandelate (SHM) to 4-hydroxy phenylacetic acid (HPA), a Tenormin intermediate, as a potential replacement for the existing Zn(Hg) reduction process. 

Divalent chromium salts show very strong reducing properties. They are prepared by reduction of chromium(III) compounds with zinc [187] or a zinc-copper couple and form dark blue solutions extremely sensitive to air. Most frequently used salts are chromous chloride [7SS], chromous sulfate [189], and less often chromous acetate. Reductions of organic compounds are carried out in homogeneous solutions in aqueous methanol [190], acetone [191], acetic acid [192], dimethylformamide [193] or tetrahydrofuran [194] (Procedure 37, p. 214). 

Although primary and secondary nitro compounds may be converted, respectively, to aldehydes and ketones by consecutive treatment with alkalis and sulfuric acid (Nef s reaction) the same products can be obtained by reduction with titanium trichloride (yields 45-90%) [565] or chromous chloride (yields 32-77%) [190]. The reaction seems to proceed through a nitroso rather than an aci-nitro intermediate [565] (Scheme 54, route b). 

Iron in acetic acid at 100° reduced 4-nitropyridine oxide quantitatively to 4-aminopyridine [170], and 3-bromo-4-nitropyridine oxide to 3-bromo-4-aminopyridine in 80% yield [170]. Chromous chloride, on the other hand, failed in the deoxygenation of nitropyridine oxides and nitroquinoline oxides [191]. 

Acetylenic aromatic acids having the triple bond Hanked by carboxyl and an aromatic ring were partially reduced to olefinic aromatic acids by chromous sulfate in aqueous dimethylformamide at room temperature in high yields. Phenylpropiolic acid afforded irani -cinnamic acid in 91% yield [195]. Its sodium salt in aqueous solution gave on catalytic hydrogenation over colloidal platinum at room temperature and atmospheric pressure 80% yield of cis-cinnamic acid if the reaction was stopped after absorption of 1 mol of hydrogen. Otherwise phenylpropanoic acid was obtained in 75-80% yield [992]. 

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